I'm sorry you are going through this trying to find your sister. I'm the one who originally looked for the domestic violence records (I'm a retired fed, so have some experience trying to find people that didn't want to talk to me about a active investigation).
You mentioned the boyfriend's name being provided with details, but I'm not seeing it anywhere on the thread, I only searched for your sister. If the police were called out but no charges were filed it likely won't be in the court system. One would have to get a copy of the actual police report and that is normally something a family member requests based on FOIA (Freedom of Information Act) laws. (you probably already know this, so my apologies if you do).
Per the websleuths rules, until they are formally named a person of interest we can't sleuth for posting any other party other than the missing person. So even if I had the boyfriends name, I can't share any information about him on a public thread.
Ohio doesn't have a central database for criminal records (Like Indiana does), so it usually requires a county by county search, and not all counties have information available TO THE PUBLIC and not all courts, so it makes it tough without a lot of detail. All I had was her name and age.
So if you have a specific city she was a resident in Ohio other than Mansfield perhaps, that might help. If she was just staying with him and it wasn't her formal place of residence,
it should still show up in a court record, simply listing her address in Mississippi (or elsewhere).
To ensure that factual information is discussed on WS, links to MSM reports or LE statements are required for statements made as fact.
The exception to this rule is when we have a Verified Insider who is a family member (or friend of the victim or missing person.) I might suggest you look into becoming verified so that you can share with us details that otherwise might not be known.
The Verified Insider process is completely confidential and details can be found here: Verification Process for Professional or Insider Posters